Register a SA Forums Account here!
JOINING THE SA FORUMS WILL REMOVE THIS BIG AD, THE ANNOYING UNDERLINED ADS, AND STUPID INTERSTITIAL ADS!!!

You can: log in, read the tech support FAQ, or request your lost password. This dumb message (and those ads) will appear on every screen until you register! Get rid of this crap by registering your own SA Forums Account and joining roughly 150,000 Goons, for the one-time price of $9.95! We charge money because it costs us money per month for bills, and since we don't believe in showing ads to our users, we try to make the money back through forum registrations.
 
  • Post
  • Reply
The Muffinlord
Mar 3, 2007

newbid stupie?

The Muffinlord posted:

I wasn't planning to use much more than 5 on it; I mostly just want to hear as well as I can be heard without having to use my RTL-SDR for receive audio. But as it turns out, the screw it has for a tripod mount doesn't match the cheap camera tripod I've had lying around for ages, so this may be a wash if I can't get the drat thing mounted properly.

It was a wash. I guess I got a defective one, cause it wouldn't mount to a camera tripod more than one single turn without locking up so hard I couldn't turn it with a screwdriver and a wrench, much less by hand. I've returned all the poo poo and I'll do what I should have done anyway, wait for my performance balance from work in like a month and then just buy a really good one from a name brand.

Adbot
ADBOT LOVES YOU

Coxswain Balls
Jun 4, 2001

I'm trying to view the hydrogen line by following this paper as a base, and so far I've got the thing bashed together at least. It was snowing today so I couldn't set it up outside, but it's working well enough to triangulate some spurious emissions on 1419 MHz somewhere on campus. If I want to fine tune things more it sounds like I need a VNA, but I'm not sure which one I should get. NooElec has the NanoVNA H4 and the NanoVNA v2 SAA2 for the same price ($163 CAD), and while it seems like I should just go with the latter because it has a higher frequency range, I'm sure there must be more to it than that which I'm missing.

The guys in the microwave lab seem pretty interested in what I'm doing, but I couldn't work up the nerve to ask them if I can hook a piece of cookware up to a $100k Agilent VNA.

drunk mutt
Jul 5, 2011

I just think they're neat

Coxswain Balls posted:

I'm trying to view the hydrogen line by following this paper as a base, and so far I've got the thing bashed together at least. It was snowing today so I couldn't set it up outside, but it's working well enough to triangulate some spurious emissions on 1419 MHz somewhere on campus. If I want to fine tune things more it sounds like I need a VNA, but I'm not sure which one I should get. NooElec has the NanoVNA H4 and the NanoVNA v2 SAA2 for the same price ($163 CAD), and while it seems like I should just go with the latter because it has a higher frequency range, I'm sure there must be more to it than that which I'm missing.

The guys in the microwave lab seem pretty interested in what I'm doing, but I couldn't work up the nerve to ask them if I can hook a piece of cookware up to a $100k Agilent VNA.



It's a tool that analyzes, if they seem interested just ask as the worst is they just nope out.

As far as the NanoVNA, it is a nifty lil tool that plays nicely for things like this (just use the software instead of the builtin interface) so that also is an option. Don't know if there are cheaper versions that might work and am now starting to wonder if my "NanoVNA" was even done by Nooelec.

yoloer420
May 19, 2006

I have nothing to input in regards to your questions, but I read this article sometime ago and thought it might be useful.

Coxswain Balls
Jun 4, 2001

Thanks for the tips. The one I picked up came in and I've been having fun testing all my antennas. I think I got the hang of it but I'm wondering if I'm missing any critical steps for using it properly. The first time I hooked it up to the radiotelescope I got this reading.



That seems way too good to be true for my very first try at building the dipole with a 1/4 wave balun with no measuring tools other than a ruler. The reason I ask if I'm doing it right is because the coax inside the antenna mast broke and I had to rebuild it (didn't have proper strain relief, my bad), and now when I'm testing things my return loss isn't anywhere near as good nor is it centred in the right area (around a hundred-ish MHz off). As I'm testing it now, the VNA is connected much closer to the antenna (just a little below the balun), whereas before there was around two feet of coax before soldering on a connection.

I was originally connecting all of the calibration standards directly to the VNA port before hooking up the feed line to the antenna. Am I correct in assuming that was going about it the wrong way, which explains the almost perfect values in the above image at my target frequency? I'm using all the same parts and the only thing different is shorter coax and cutting a new balun.

Jonny 290
May 5, 2005



[ASK] me about OS/2 Warp
coax loss cloaks bad SWR. previously your signal was attenuated on the way to the antenna, and again on the way back. so say your coax loss is 3db. the signal loses 3db at the antenna and the reflected wave has another 3db of loss. even if you completely unhooked the antenna you'd never see more than 3:1 SWR (6db return loss). Now lets say its a looong run with 10db of loss. 20 db return loss. 1.2 SWR.

this is one trick shady sellers of the G5RV multiband HF antenna use. They claim "you gotta feed it through at least 50 feet of rg8x, don't use good coax". theyre hiding the bad swr with coax loss. its just being burnt up as heat. not an actual Good Match.

Coxswain Balls
Jun 4, 2001

Fantastic, I think now I can safely assume that the values I'm getting now are realistic numbers that I was probably dealing with from the start and now I have to put some work in to center it onto my band of interest. To be honest, I was kind of disappointed when I first hooked it up and it looked that good, I really wanted to have to use the VNA to get it tuned and learn while doing so, and now it looks like I'll have that chance. I feel like I need to be less sloppy with the balun, but the chunk of dremeled PCB I'm mounting stuff too is also pretty janky.

The Muffinlord
Mar 3, 2007

newbid stupie?

Jonny 290 posted:

coax loss cloaks bad SWR. previously your signal was attenuated on the way to the antenna, and again on the way back. so say your coax loss is 3db. the signal loses 3db at the antenna and the reflected wave has another 3db of loss. even if you completely unhooked the antenna you'd never see more than 3:1 SWR (6db return loss). Now lets say its a looong run with 10db of loss. 20 db return loss. 1.2 SWR.

this is one trick shady sellers of the G5RV multiband HF antenna use. They claim "you gotta feed it through at least 50 feet of rg8x, don't use good coax". theyre hiding the bad swr with coax loss. its just being burnt up as heat. not an actual Good Match.

Is there anything that can be done to remediate this? I managed to get an actually good mag loop(Chameleon F-Loop 3.0 Plus, a hell of a step up from the aliexpress special I was trying out before) once my annual bonus from work came in, and slapped 50 feet of coax on it so that I could maybe move it further away from the rest of my stuff. It's performing pretty well(I'll have to go back for the remote tuning motor, though), but I noticed that compared to the 12-ft coax it came with, the 50 feet line has a way flatter SWR curve, capping out at around 4:1 instead of 10:1, and with a way wider "bottom" area where it's at 1:1. Not that I'm one to complain about mysteriously "better" performance, but it seems suspect, in light of what you're saying. I'd feel better using it knowing that I'm not accidentally dumping waste heat into an expensive-rear end high voltage capacitor, or cooking off my feed line either.

I love the antenna, though! I should have done this from the start. I've got the rigid aluminum ring on it, and it straight up looks like something a mad scientist would use, and can throw my lovely basement signal all the way across the Atlantic.

Jonny 290
May 5, 2005



[ASK] me about OS/2 Warp
Better coax. The fatter the better and you want teflon.

"LMR400" is the standard i use - back before the economy poo poo the bed, i picked up a 1000 foot spool of Shireen RFC400 which is basically the same as the Times Microwave stuff, ran everything i ever wanted and still have like 250 feet left over. Best $400 i ever spent on ham radio.

Coxswain Balls
Jun 4, 2001

Here's where I'm at so far, checking to see if I'm still doing things right.



I ran across this page while looking for tips on tuning a hydrogen line dipole, and he was having similar issues with the target frequency being lower than expected for the element dimensions. Apparently he wasn't taking velocity factor into account so he cut it a bit shorter until things lined up nicely.

That worked up to an extent for me, but it still wasn't looking great at 1.42 GHz. I figured maybe I also needed to take velocity factor into account for the ¼λ balun. My best guess for the RG-174/U I got out of a scrap pile was a velocity factor of 0.66, so I shortened it by that amount and got the much better values in the picture. When looking online I'm seeing people say that velocity factor shouldn't matter for a Pawsey stub but it appears to be having some effect on mine. I don't know what I'm doing! Antenna design is fun, but hard!

Coxswain Balls
Jun 4, 2001



Went back to a 5.3cm balun after putting it in the reflector. It's so sensitive to movement and positioning, but I think this is the best I'm going to get. That sharp drop still seems suspect to me, but it's a very short coax now so I don't know what else it could be.

Big Mackson
Sep 26, 2009
Built a cubical quad yagi yesterday. should have used thinner copper wire then it would have been easier to make a rectangle out of it.
i dont know the science behind it but a common mode choke 1:1 balun made swr better.




edit: ITS TAPE!
edit2: drilling by hand makes it difficult to have a true straight through alignment for the wooden garden sticks. had to stick pieces of bamboo to adjust the sticks.

Big Mackson fucked around with this message at 14:50 on Feb 28, 2024

BONESAWWWWWW
Dec 23, 2009


Antennas are basically magic to me. I've never heard of a cubical quad before. Looks great! What's the use case? Or is it just for fun?

Big Mackson
Sep 26, 2009

BONESAWWWWWW posted:

Antennas are basically magic to me. I've never heard of a cubical quad before. Looks great! What's the use case? Or is it just for fun?

its just like a yagi but teoretically it would perform a little better.


The antenna i made is for 2 meter vhf band. Tested it with winlink packet and it worked great.
It is relatively easy to switch between horizontal and vertical polarization by just moving the feed point from the vertical stick to the horizontal stick.
or maybe i can make some complicated dual feed setup for remote switching idk. something like that is probably invented in like 1910, like almost all other radio tech lol.

edit: at higher frequencies you can buy antennas like that but it is a circle instead. here is a high weed thought. magnetic loops. array stacked. O_O
Someone make the science right now!

Jonny 290
May 5, 2005



[ASK] me about OS/2 Warp
i had a 4 element quad my dad helped me build out of pvc pipe that we stuck on a tv rotator on our chimney about 30 feet up. I could hit repeaters like 100 miles away with five watts. good poo poo

drunk mutt
Jul 5, 2011

I just think they're neat
Isn't the "quad" setup something that is good for things like EME/Meteor scatter type work?

Big Mackson
Sep 26, 2009

drunk mutt posted:

Isn't the "quad" setup something that is good for things like EME/Meteor scatter type work?

if i get a longer boom i might try 9 element quad yagi and see if it might work for such things.

manero
Jan 30, 2006

LimaBiker
Dec 9, 2020




Okay we need a digimode now that literally sounds like farts but actually has data/text encoded in the flatulence.

I suggest we call it Flatulencia.

Motronic
Nov 6, 2009

Fahrtscriber

Radio Nowhere
Jan 8, 2010
shTTY

Jonny 290
May 5, 2005



[ASK] me about OS/2 Warp
THROB is a really neat sounding mode, as it actually is a volume ramp-up/ramp-down on each tone. Very eerie and what average people would consider to be "UFO noises"

Progressive JPEG
Feb 19, 2003

hamstep: binary mode where a fast wub is 0 and a slow wub is 1

Empty Pockets
Jun 11, 2008

Progressive JPEG posted:

hamstep: binary mode where a fast wub is 0 and a slow wub is 1

don't forget the kick + snare timing signals

Big Mackson
Sep 26, 2009
new craze have hit the music market.

uuuiiiuuuiiiuuuiiiiiiiiuuuuuuooooooooiiiiiiiiiuuuuuu

WOW!

Coxswain Balls
Jun 4, 2001

https://burningjustice.net/diy/wokscope/timelapse_01.mp4

Found out that it's relatively radio quiet in a friend's backyard so I set up there to collect data for 12 hours. Very happy with the results, even with the weird noise floor fluctuations going on. That spike at 1420.8 MHz seems to be an artifact from either the LNA or the SDR, but when it spikes up everything else drops. Might also be temperature related? Plenty of room for more experimentation, overall I'm pleased with imaging two areas that are redshifting and blueshifting so I can make some velocity calculations.

The university is offering to reimburse me for parts because they want to make it part of their honours lab curriculum starting next year, which feels great. My lab report is going to double as a lab manual for the honours lab physics students next year, so while my statistical analysis capabilities are a bit rough I hope I can pull it together to make something decent. The actual procedure, theory, and construction stuff I have a good handle on and had a lot of fun with it so hopefully I can get my poo poo together to properly calculate my uncertainties and distributions.

I already have a friend who wants me to do a guest talk at her high-school's science club so I'll also be preparing that, and when I'm collecting data in a park or other similarly radio-quiet area I get lots of interest and questions. It's like when I used to do outreach for astronomy, but because it's radio you can do it during the day which helps a lot with outreach type stuff.

Adbot
ADBOT LOVES YOU

Big Mackson
Sep 26, 2009
Its difficult to find crossover plate with u shaped fasteners or something in norway. It looks like vertikal to horizontal antenna mounting products died when people just use internet and not yagi antennas :/

or i just dont know what kind of norwegian words we use for such things.

  • 1
  • 2
  • 3
  • 4
  • 5
  • Post
  • Reply